1. Field of the Invention
This invention relates to an image reading apparatus.
2. Description of Related Art
The construction of a conventional image reading apparatus will hereinafter be described with reference to FIGS. 12 to 14 of the accompanying drawings.
In FIG. 12, the reference numeral 1201 designates an image reading apparatus (hereinafter referred to as the image scanner) for reading an image, and the reference numeral 1202 denotes an auto document feeder (hereinafter referred to as the ADF) for automatically successively feeding a plurality of originals one by one.
The reference numeral 1203 in the image scanner 1201 designates copy board glass, and an original 1204 is placed on the copy board glass 1203 and a desired image is read. The procedure of reading the image will hereinafter be described briefly.
The reference numeral 1205 denotes a light source for applying light to the original, and generally when the read image is to be outputted in black and white, a yellow green light source is used, and when the read image is to be outputted in colors, a white light source is used. As the kinds of the light source, various kinds of light sources such as a cold cathode tube, a halogen lamp and a xenon lamp are used depending on the uses thereof.
Reflected light 1206 applied from the light source 1205 to the original is reflected by a first mirror 1207, a second mirror 1208 and a third mirror 1209, is condensed by a lens unit 1210 and is imaged on a CCD 1211 which is a photoelectric conversion element.
The light information of the imaged light is converted into a voltage by the CCD 1211, is further converted from an analog signal to a digital signal, and thereafter is subjected to a series of correcting processes such as shading correction, black level correction and gamma correction, and is outputted to a monitor, a file or the like.
The constituents from the light source 1205 to the CCD 1211 are constituted as a carriage unit 1212 by a unit. A reading optical system thus containing the constituents of the optical system in a carriage unit, if dimensional accuracy in the carriage unit 1212 is controlled, has the merit that the quality of the read image is not spoiled even if other dimensional accuracy is not finely controlled.
Also, the reference numeral 1213 designates a white reference plate constructed at a location which cannot be seen from an original placing surface, and upon closing of a power source switch or at the timing immediately before image reading, the light source 1205 is turned on and the white reference plate 1213 is read to thereby detect the offset gain adjustment of an A/D converter (not shown) for converting the analog voltage photoelectrically converted by the CCD 1211 into a digital voltage, and the trouble of the light source 1205.
As the popular construction of another reading optical system, there is a 1 to ½ optical system shown in FIG. 13. This reading optical system is of a construction in which a first optical unit 1301 including a light source 1205 and a first mirror 1207, and a second optical unit 1302 including a second mirror 1208 and a third mirror 1209 are movable units, and a lens unit 1210 and a CCD 1211 are fixed. Since the moving speeds of the first optical unit 1301 and the second optical unit 1302 are designed to be 1:½, this reading optical system is called the 1 to ½ optical system. By being designed at such a speed ratio, the distance from a reading position to the CCD is always constant at a+L1+L2+b. This reading optical system has a merit in depth of focus because the distance between an object and an image can be secured long, while on the other hand it becomes necessary to sufficiently control the dimensional accuracy of the entire scanner.
The carriage unit 1212 or the first optical unit 1301 and the second optical unit 1302 are one-dimensional reading units which can read an image of a predetermined width (84.7 μm at 300 dpi). A one-dimensional image read thereby can be read as the two-dimensional image of the entire original by connecting together images one-dimensionally read while the carriage unit 1212, the first optical unit 1301 and the second optical unit 1302 are moved by a motor (not shown). After the image of the entire original has been read, it is outputted to a personal computer or a monitor or the like.
As described above, an original like a photograph which cannot be bent, a thick original such as a book, or an original to be read with a high quality of image usually has its image read while being place on the copy board glass. On the other hand, for the reading of a plurality of original sheets, there has been carried out a method of collectively reading images by the use of the ADF 1202. It should be noted that in some cases, the carriage unit 1212 is constituted by a CIS module.
The reference numeral 1214 denotes an ADF open detection sensor for detecting whether the ADF 1202 is opened or not.
The detailed construction of the ADF 1202 will now be described with reference to the construction view of FIG. 14.
The reference numeral 1401 designates an original tray for stacking originals 1402 thereon, and the originals 1402 are stacked on the original tray 1401 with images to be read facing upward. The reference numeral 1403 denotes a sheet presence or absence detection sensor for detecting the presence or absence of the originals 1402 on the original tray 1401, and it is designed to use a photointerrupter and a mechanical flag to detect the state thereof. When the start of reading is executed with the originals 1402 stacked on the original tray 1401, a conveying roller 1404 is driven for only one full rotation by a solenoid, and only one of the originals is conveyed into the conveying path of the ADF 1202. The thus conveyed original 1402 is formed into a predetermined loop by a registration roller 1405, and the leading edge of the original 1402 conveyed into the ADF 1202 is detected by a leading edge detection sensor 1406. The reference numeral 1407 designates a photointerrupter which is an original leading edge detection sensor, and it is linked with the leading edge detection sensor 1406 by a mechanical flag, and design is made such that the leading edge of the original 1402 pushes out the mechanical flag, whereby the photointerrupter 1407 is shielded from light. The original 1402 is further conveyed into the interior of the ADF 1202 along the circumference of an original roller 1409 while being nipped between a first conveying roller 1408 and the original roller 1409 and between a supporting unit 1410 and the original roller 1409, and the reading of the image of the original 1402 is started at the timing whereat the original 1402 arrives at Mylar 1411. This timing is judged in a predetermined time after the leading edge detection sensor 1406 has detected the leading edge of the original, or if a stepping motor is used as the motor, by predetermined pulses having elapsed after the leading edge sensor 1406 has detected the leading edge of the original.
The original 1402 of which the image has been read from the leading edge is delivered onto a discharging tray 1413 by a second conveying roller 1412, and the reading of the first original is terminated.
The second and subsequent originals are fed in a predetermined time after the leading edge detection sensor 1406 has detected the leading edge of the original 1402, or if a stepping motor is used as a drive source for conveying sheets, a solenoid is driven at such timing that they are fed after the lapse of predetermined pulses, and the above-described control is continued until the sheet presence or absence detection sensor 1403 comes to detect no original on the original tray 1401.
Also, if there is no change in the result of detection even when a predetermined time has elapsed after the leading edge detection sensor 1406 has detected the leading edge of the original 1402, control is effected so that it may be treated as jam.